This is an easy situation to get out of -- in my experience most Honda engines have this issue, on at least one of the three studs, if not all of them. Just simply keep unscrewing the nuts - the stud underneath will unscrew from the top of the engine, but that is OK. It is best to work each of the three nuts a few turns at a time in sequence, to keep the shroud fairly even as the studs unscrew. If you want, when the shroud comes off, clamp the stem of the stud with locking pliers while attempting to turn the nut off, to separate them. There is really no need to do this though. On reassembly, just screw in the studs to the engine again by turning the nuts. Applying some thread lock to the lower stud thread might allow the nut to be removed from the top of the stud next time. Let me know if that works with your motor; I've seen many of these and it is a common issue. No need to destroy anything!